A novel sampling method for assessing human-pathogen interactions in the natural environment using boot socks and citizen scientists, with an application to the seasonality of Campylobacter

This paper introduces a novel method for sampling pathogens in natural environments. It uses fabric boot socks worn over walkers' shoes allowing collection of composite samples over large areas. Wide area sampling is better suited to studies focussing upon human exposure to pathogens (e.g. recreational walking). This sampling method is implemented using a Citizen Science approach: groups of three walkers wearing boot socks undertook one of six routes, 40 times over 16 months in the North West (NW) and East Anglian (EA) regions of England. To validate this methodology we report the successful implementation of this Citizen Science approach, the observation that Campylobacter was detected on 47% of boot socks, and the observation that multiple boot socks from individual walks produced consistent results. Findings indicate elevated Campylobacter presence in the livestock dominated NW in comparison to EA (55.8% vs 38.6%). Seasonal variation in Campylobacter presence was found between regions, with indications of winter peaks in both regions, but a spring peak in NW. Campylobacter presence on boot socks was negatively associated with ambient temperature (p=0.011) and positively associated with precipitation (p<0.001), results which are consistent with our understanding of Campylobacter survival and the probability of material adhering to boot socks. C. jejuni was the predominant species found, with C. coli largely restricted to the livestock dominated NW. Source attribution analysis indicated that the potential source of C. jejuni was predominantly sheep in NW and wild birds in EA but did not vary between peak and non-peak periods of human incidence. Importance There is debate in the literature on the pathways through which pathogens transfer from the environment to humans. We report on the success of a novel method for sampling human-pathogen interactions using boot socks and citizen science techniques, which enable us to sample human-pathogen interactions that may occur through visits to natural environments. This contrasts with traditional environmental sampling, which is based upon spot sampling techniques and does not sample human-pathogen interactions. Our methods are of practical value to scientists trying to understand transmission of pathogens from the environment to people. Our findings provide insight into the risk of Campylobacter from recreational visits and an understanding of how these risks vary seasonally and the factors behind these patterns. We highlight the Campylobacter species predominantly encountered and the potential sources of the C. jejuni.